Neglected Tropical Diseases (NTDs): Characteristics, List of NTDs, Causative Agents, Transmission, Prevention and Control

Table of Contents

Introduction

Neglected Tropical Diseases (NTDs) are a group of infectious diseases, prevalent in the tropical areas, that cause substantial illness and impair physical and cognitive impairment.
Neglected tropical diseases (NTDs) are a diverse group of 20 conditions that are mainly prevalent in tropical areas.
Neglected Tropical Diseases (NTDs) are especially common in low-income populations in developing regions of Africa, Asia, and the Americas.
Neglected Tropical Diseases (NTDs), are called “neglected” because they generally affect the world’s poor population but are yet to receive as much attention as other diseases.
Likewise, as the name suggests, NTDs are mainly prevalent in the tropical areas where they affect impoverished, underserved communities and disproportionately affect women and children.
It includes diverse groups of tropical infections mostly prevalent in the low-income countries in the region of Africa, Asia and Americas.
It primarily affects the poorest of poor living in the remote rural communities and deprived urban populations mainly in the subtropical region.
It is more prevalent in the areas where people have no access to clean water or safe ways to dispose human waste.
Dengue, lymphatic filariasis, trachoma, leishmaniasis, etc. are few examples of NTDs.

Key Facts about Neglected Tropical Diseases (NTDs)

Neglected Tropical Diseases (NTDs) are widespread in the world’s tropical regions, where poorest community resideand quality of water safety, sanitation, and access to health care are substandard.
Some of the NTDs are also found in some areas of United States (US) and other developed nations where there are high levels of poverty.
About 1 billion people—approximately one-sixth of the world’s population—suffer from at least one NTD.
NTDs are called “neglected” because they generally are not considered public health problems in developed nations and have not received as much attention as other diseases from the past.
Some NTDs are found in parts of the United States, especially among impoverished minorities.
NTDs comprise several diseases that have a range of effects, from extreme pain to permanent disability to death. Here are some examples:
- Ascariasis: Caused by the soil-transmitted roundworm Ascaris lumbricoides, it can impair growth and cognition.
- Leishmaniasis: A parasitic disease transmitted by infected sand flies, it can cause skin ulcers or lesions and swelling of the spleen and liver.
- Leprosy (Hansen’s disease): A chronic infectious disease caused by bacteria,that can cause permanent damage to the skin, nerves, limbs, and eyes.
- Lymphatic filariasis (elephantiasis): A parasitic worm disease spread by mosquitoes, lead to disfiguring swelling of the legs, scrotum, and breast.
- Onchocerciasis (river blindness): Spread from by infected black flies, it can cause extreme itching, blindness, and skin lesions. It is a parasitic worm disease
- Trachoma: Caused by the bacterium Chlamydia trachomatis, can lead to scarring of the inside of the eyelid and blindness.
Despite their prevalence around the world, most NTDs are relatively easy to treat and can be prevented.
In addition to significant mortality and morbidity – approximately 200,000 deaths and 19 million Disability Adjusted Life Years (DALYs) is lost annually
Historically, NTDs have ranked very low and almost absent from the global health policy agenda – only to gain recognition in 2015 with the Sustainable Development Goals (SDG target 3.3).
Every year January 30 is celebrated as World NTD (Neglected Tropical Disease) day.

Characteristics of Neglected Tropical Diseases (NTDs)

NTDs affect the poorest people who have poor access to safe water, sanitation, good hygiene and basic health services.
NTDs are chronic and slowly developing.
They rarely cause death.
NTDs can cause severe pain and life long disabilities.
Disabilities caused by NTDs are usually irreversible.
A person can be affected by more than 1 NTD at the same time.

List of Neglected Tropical Diseases (NTDs)

Currently, WHO has classified following 20 infectious diseases as Neglected Tropical Diseases (NTDs). They are:

Buruli ulcer: debilitating skin infection causing severe destruction of the skin, bone and soft tissue.
Chagas disease: infection transmitted through contact with vector insects, ingestion of contaminated food, infected blood transfusion, congenital transmission, organ transplantation or laboratory accidents.
Dengue and chikungunya: mosquito borne viral disease which causes flu like illness.
Dracunculiasis (Guinea-worm disease): nematode infection transmitted by drinking-water contaminated with parasite-infected water fleas.
Echinococcosis: infection caused by larval stages of tapeworms forming pathogenic cysts. Transmitted to humans through ingestion of eggs, shed in feces of dogs and wild animals.
Food borne trematodiases: infection acquired by consuming fish, vegetables and crustaceans contaminated with larval parasites.
Human African trypanosomiasis (sleeping sickness): parasitic infection spread by bites of tsetse flies. Almost 100% fatal if not diagnosed and treated immediately.
Leishmaniasis: transmitted through the bites of infected female sandflies. In severe cases, it affects internal organs, and causes face ulcers, disfiguring scars and disability.
Leprosy (Hansen’s disease): caused by infection mainly of the skin, peripheral nerves, mucosa of the upper respiratory tract and eyes.
Lymphatic filariasis: Infection transmitted by mosquitoes causing abnormal enlargement of limbs and genitals from adult worms inhabiting and reproducing in the lymphatic system.
Mycetoma: debilitating, disabling bacterial/fungal skin infection thought to be caused by the inoculation of fungi or bacteria into the subcutaneous tissue.
Chromoblastomycosis and other deep mycoses
Onchocerciasis (river blindness): parasitic eye and skin disease, transmitted by the bite of infected blackflies. Onchocerciasis causes severe itching and eye lesions, leading to visual impairment and permanent blindness.
Rabies: viral disease transmitted to humans through the bites of infected dogs
Scabies and other ectoparasites
Schistosomiasis: It is a larval worm infection. Transmission occurs when larval forms released by freshwater snails penetrate human skin during contact with infested water.
Soil-transmitted helminthiases: group of intestinal helminth infections transmitted through soil contaminated by human feces.
Snakebite envenoming
Taeniasis/cysticercosis: infection by tapeworms in human intestines;
Trachoma and yaws and other endemic treponematoses

Agents Responsible for NTDs

The infectious agents responsible for NTDs are:

Viruses (rabies and dengue)
Bacteria (leprosy, yaws, trachoma and Buruli ulcer)
Protozoa (leishmaniasis and trypanosomiasis)
Helminth parasites (schistosomiasis, lymphatic filariasis, onchocerciasis, intestinal worms and Guinea worm).
Fungi
Ectoparasites

Mode of Transmission of NTDs

NTDs can be transmitted through:

flies, fomites (e.g., skin cells, hair, clothing or bedding) and fingers (trachoma)
mosquitoes (dengue fever and filariasis)
tsetse flies (sleeping sickness)
sandflies (leishmaniasis)
blackflies (onchocerciasis)
snails, which release infective larvae into water to penetrate human skin (e.g., schistosomiasis)
the faeco-oral route (e.g., soil-transmitted helminths) or via food products etc.

NTDs That Can be Controlled or Eliminated

Among the 20 NTDs, following 6 (six) NTDs can be controlled or even eliminated through mass administration of safe and effective medicines or other, effective interventions:

Dracunculiasis (Guinea Worm Disease)
Lymphatic Filariasis
Onchocerciasis
Schistosomiasis
Soil-transmitted Helminths (STH) (i.e., Ascaris, Hookworm, and Whipworm)
Trachoma

Importance of Addressing Neglected Tropical Diseases (NTDs)

NTDs have taken a tremendous toll on the global health. 1 out of every 6 people are suffering from at least one NTD.
WHO estimates that over 1.7 billion of the world’s population should be targeted by prevention and treatment activities for at least one of these diseases, every year.
NTDs affect the people residing on the tropical region, especially the ones who live in poverty because it is especially related to the environment conditions that people live in.
Although NTDs rarely lead to death, it can cause significant disability that lasts for a lifetime. Disabilities may include blindness, neurological problems, disfigurement etc.
When this disease exists in area, the whole population around are at risk and since it is transmitted usually through vector, it doesn’t take much time to spread around
Not only addressing NTDs is important but alleviating poverty and strengthening health system alongside is necessary to eliminate NTDs.
About 1.7 billion are infected globally and with addition of COVID-19 pandemic the threat of its rise is still there.
NTDs degrade the quality of life and consequently pull the trigger of ‘cycle of poverty’ among the disadvantaged populations as they can:
- Impair intellectual development
- Reduce school enrollment
- Hinder economic productivity by limiting the ability to work
The COVID-19 pandemic has taken the toll on economy and if NTDs are not tackled the condition can even get worse.
Unlike other disease NTDs can be treated through cost effective interventions and has many ripple benefits.
Eliminating these diseases in endemic countries can be effective for achieving larger health populations’ health outcomes and improve quality of life.
Combating Neglected Tropical Disease ensures that no one is left behind and every individual has equal chance to achieve their goals.
Thus,the goals of SDG to eradicate poverty and hunger and strengthening education and equality can be achieved only through ending NTDs

Preventive and Control Measures for NTDs

WHO’s Ending the neglect to attain the Sustainable Development Goals: a road map for neglected tropical diseases 2021−2030 describes five broad NTD interventions with the aim of controlling, preventing and/or eliminating 20 NTDs.

The road map focuses on integrated cross-cutting approaches rather than vertical disease programs.

Five broad Neglected Tropical Disease (NTD) interventions are:

1. Preventive Chemotherapy and transmission control (PCT)

It includes the strategy to ensure availability of safe and effective drugs that is feasible to implement large scale preventive chemotherapy
It focuses on providing national programmes for implementation of national elimination and control activities where preventive chemotherapy is the main tool
It also advocates for coordinate approach to preventive chemotherapy

2. Innovative and Intensified disease management

It focuses on the diseases for which cost-effective controls do not exist and where large scale use of existing tools is limited
It focuses on managing the disease in primary health center
Its main strategy is to enhance NTD control through combining expertise in disease-specific areas with cross-cutting issues such as surveillance, capacity building, advocacy and research

3. Vector ecology and management

It focuses on development of strategies and guidelines based on principles and approaches of integrated vector management
This is an important component in the prevention and control of vector-borne disease.
It focuses on effective methods of targeting mosquitoes, flies, ticks and other vectors that are responsible for transmitting the pathogens.
Guidelines and strategies for the sustainable and cost-effective application of vector control interventions is necessary for management of vector.

4. Safe Water, sanitation and hygiene (WASH)

Access to safe water, sanitation and hygiene is a priority intervention of WHO.
The intervention plays a vital role preventing and curing all NTDs.

5. Veterinary public health services

Veterinary public health services identify that health of the people is connected to the health of the animals and the environment.
It focuses on health of the animals and the environment as they play a major role in ensuring good health of the people.